Method of running an air inlet system

ABSTRACT

The present embodiments disclose a method of running an air inlet system upstream of one or more inlet air filters of a device protected by air filtration, wherein the method comprises: regulating the relative air humidity of the inlet air at the one or more inlet air filters in dependence of the inlet air filters differential pressure.

FIELD OF THE INVENTION

The present invention relate to a method of running an air inlet systemupstream of one or more inlet air filters of a device protected by airfiltration. In particular, the present invention relates to foggingsystems for the cooling of inlet air to a gas turbine, diesel engine,process blower, or other motive force. Additionally, these embodimentsrelate to the method of control for these fogging systems.

BACKGROUND OF THE INVENTION

Gas turbines and diesel engines provide motive force by compressing anear constant volume of air and igniting fuel to generate shaft power.This power may be used to drive generators used in the production ofelectricity or may be used to drive compressors or blowers used in oiland gas transmission or other processes. When the ambient airtemperature rises, the density of the air decreases, causing the massflow through the gas turbine to also decrease. The consequence of theseis that as ambient temperature increases the gas turbines and dieselengines are prone to loss of output, while the fuel rate increases.Typically, gas turbines will lose about 0.7% to about 0.9% of theirrated power output for each degree Celsius of inlet temperatureincrease.

Presently, the solution to this widespread problem is to install aninlet cooling system to redress the inlet air temperature. Commonmethods for this reduction in temperature include: the installation ofcooling coils; the installation of media-type evaporative coolers; and,the installation of fogging systems, which generally cool the airtemperature through the evaporation of water sprayed into the systemfollowing the filter stage. However, each of these types of systems hascertain disadvantages.

Cooling coils and the associated plant are expensive, and provide anadditional level of complexity to plant operations. Further, these typesof systems cause a pressure differential in the air stream even when notin use.

Media-type evaporative coolers are relatively simple, but they cannot beadjusted to accommodate for changes in ambient air conditions.Additionally, the media used in these systems is prone to damage, andalso presents a cause a pressure differential in the air streamyear-round. Further, maintenance or replacement of media requires thatthe gas turbine or other downstream process be shut down.

Fogging systems introduce fog, in the form of water droplets, into theair. The introduced water droplets may then evaporate into the air,which creates a new equilibrium—a lower temperature and a higherrelative humidity. From any given starting point, the system enthalpyremains unchanged; and, a temperature between the initial ambienttemperature and the corresponding wet bulb temperature may be achievedby limiting the amount of water available. This process, known asfogging, is known and used in the art to combat the loss of power outputthat occurs when the ambient temperature increases. However, state ofthe art systems have many limitations and disadvantages. In order toaddress some of these limitations and disadvantages, the presentdisclosure splits fogging into two separate stages (one located beforethe filter, and one after the filter), and provides separate controlsystems for each stage of fogging.

Some early state of the art fogging systems were located upstream ofinlet filters. Due to issues of increased filter pressure drop, currentstate of the art locates fogging systems downstream of the final stageof filtration. These current state of the art fogging systems require alarge number of downstream high pressure nozzles in the clean air stream(the air stream after filtration) in order to avoid soaking of filterelements and in order to provide enough water to traverse from ambienttemperature towards wet bulb temperature. Due to the placement of thesenozzles in the clean air stream, the system must be stopped and brokeninto, or partially disassembled, for any modifications or repairs.Further, these systems are only capable of being controlled at a coarselevel. For example, a four stage pumping system offers a resolution ofabout 25% of turndown. Additionally, these systems recommend the use ofdemineralized water in order to avoid calcification of the fine nozzleopenings. Finally, the large number of nozzles in the clean air ductpresents a risk of foreign object damage, should a nozzle or partthereof become loose and fall into the air stream, to the downstreamequipment.

Therefore, there exists a need in the art for a finely controlledfogging system that does not affect filtration performance and thatminimizes, or eliminates, hardware in the clean air duct. There exists aneed in the art for a system that can minimize, or eliminate, theutilization of demineralized water in the intake ducts. Further, suchminimization, or elimination, of the use of demineralized water wouldminimize the deleterious effects of free water that may pool of thefloor of the duct near the bell mouth of the compressor 10.

SUMMARY OF THE INVENTION

The present disclosure is particularly directed towards a method ofrunning an air inlet system upstream of one or more inlet air filters ofa device protected by air filtration, wherein the method comprises:regulating the relative air humidity of the inlet air at the one or moreinlet air filters in dependence of the inlet air filters differentialpressure. The solution according to the invention is based on the factthat in particular hygroscopic filter media and/or hygroscopiccontamination captured by the filter will increase the filterdifferential pressure, if the relative air humidity exceeds a definedvalue of relative air humidity, which is in particular about 80%relative air humidity. Therefore, it is important to control therelative air humidity as defined by the invention. Preferable it isintended to control the relative air humidity to levels below about 80%.On the other hand, the higher the inlet air humidity relative to theambient relative air humidity is, the higher is the effect ofevaporative cooling. As a result, there is an optimum set point forrelative air humidity, that needs to be controlled precisely.

The relative air humidity is preferably set to amount between 70% and90%, in particular between 75% and 85%.

The relative air humidity is further preferably set to amount about 80%.The effect of a rise of the filter differential pressure with relativeair humidity higher than about 80% becomes worse with the amount ofcontaminant loading on used filters. The difference between the filterdifferential pressure at low relative humidity and at high relativehumidity (>80%) increases with the contaminant loading. A high humidityevent could therefore trigger an alarm of a maximum differentialpressure at the respective filter. By reducing the relative air humidityto below 80%, the filter life can be prolonged, since the “wet”differential pressure level of the filter is prevented.

The relative air humidity is preferably to be set by means of a coolingsystem.

The cooling system preferably includes an evaporative cooling system.

The evaporative cooling system preferably includes a fogging system.

The fogging system preferably includes at least one rotary atomiser.This system is to be particularly advantageous when the humidity of theambient air is low, preferably lower than 80% relative humidity. Then,there is an extra strong cooling effect by evaporation of water drops ofthe at least one rotary atomiser. The invention enables to use low waterpressure and a simple nozzle design. Further, different sorts of watercan be used.

The device is preferably protected by air filtration, and the foggingsystem is preferably located upstream or downstream of one or more inletair filters. At the system according to the invention, droplet size is afunction of a rotating screen shape and its rotational speed (RPM). Itis mainly independent of the water flow rate to the rotary atomisers.Thus water flow rate can be adjusted independently, or water flow ratechanges will not affect the droplet size, thus not affecting the time itrequires for the droplets to fully evaporate. Thus according to theinvention drops will not end up in the device to be cooled or on filterswhich follow the fogging system.

The rotary atomisers according to the invention may have a high watercapacity (of approximately 3 l/min) compared to high pressure foggingnozzles (approximately 0.1 l/min). Therefore much fewer atomiser unitsare required.

The cooling system preferably includes two cooling stages, in particulara first stage fogging system upstream of one or more inlet air filtersand a second stage fogging system downstream of the one or more inletair filters. The inlet air filters can then be used to filter allremaining water drops out of the inlet air to be delivered to thedevice. If the atomisers are positioned in front of the filters, thesefilters may further filter out those solid components of the low puritywater, that would otherwise enter the turbine on fogging systemsinstalled behind the filters. At turbines, to access a clean air side ofan air intake of the turbine downstream of filters, a shut down of theturbine is required. However, scheduled shut downs of such turbines arerare. Two times per year is already often, but it could be also onlyonce every three years. For the proposed preferred system, no shut downof its turbine is required for survey of installation area, forinstallation, and for maintenance of the rotary atomisers. For thatreason, the fogging system can be installed quickly, while other coolingsystems (evaporative coolers, high pressure fogging systems, orchillers) require to wait for the next shut down to survey theinstallation area and then one has to wait for the second next shut downfor installation. During this waiting time, the proposed system isalready generation benefits and its installed capital expense is alreadypaid back, before a conventional system is even installed.

The second cooling stage preferably regulates the air humidity to beabout 100%.

The air humidity preferably is to be set by means of a heating system.The heating system is provided to adequately rise the air temperature ofthe inlet air. In case of ambient relative air humidity betweenapproximately 80% and 100% an increase in the air temperature of theinlet air could reduce the relative humidity of the inlet air at thefilters and could thereby prevent a filter differential pressure peaktriggering alarm limits. The heating system can therefore reduce therisk of an unscheduled turbine shut down.

The heating system preferably provides heat by means of warm air to bedelivered into the inlet air.

The warm air preferably includes compressor bleed air in particular of agas turbine.

Further, the warm air preferably includes exhaust air of a motive deviceenclosure, in particular a turbine enclosure.

Further preferred, the warm air includes turbine exhaust air.

Alternatively, the heating system preferably provides heat by means of aheat exchanger.

The heating system also preferably provides heat by means of a heater,in particular an electrical heater or a burner.

The device is preferably selected from a group consisting of a gasturbine, diesel engine, process blower, other motive force, or generalventilation, clean room.

The present disclosure is further particularly directed towards atwo-stage fogging system, and method for controlling said system,designed for cooling of inlet air to a gas turbine, diesel engine,process blower, other motive force, or general ventilation, clean room.The two-stage system comprises a high capacity first stage foggingsystem that is installed upstream of one or more inlet air filters,where a first stage control system prevents increase in filterdifferential pressure, and a low capacity second stage fogging systemthat is installed downstream of one or more inlet air filters, where asecond control system controls supplemental cooling to the majority oftotal air cooling of the first stage fogging system to the wet bulbtemperature. Wet bulb temperature is the temperature air would be ifcooled to complete saturation, or 100% relative humidity, by evaporationof water into the air.

In some embodiments the first stage of the system may contain aplurality of rotary atomisers with variable frequency drive, a source ofwater at low pressure, and, a modulating control valve to providevariable water quantity. In other embodiments the first stage of thesystem may contain of the above and a water holding tank with automaticlevel controls, a modulating control valve and a fixed speed or lowpressure circulating water pump.

In other embodiments the first stage of the system may contain aplurality of rotary atomisers with variable frequency drive, a source ofwater at low pressure, a water holding tank with automatic levelcontrols, and a circulating water pump with variable frequency drivethat may substantially continuously provide variable water quantity.Rotary atomisers can control the flow rate of water continuously andindependently of the droplet size. Accordingly, these sort of coolingsystem is the preferred mode of operation, when the ambient relative airhumidity is below about 80% relative air humidity. This optimizes thegas turbine efficiency and power output by the adiabatic cooling effectof the fogging system.

In still other embodiments the first stage of the system may contain aplurality of medium pressure nozzles, a source of water at low pressurea water holding tank with automatic level controls, and a circulatingwater pump with variable frequency drive that may substantiallycontinuously provide variable water quantity.

In some embodiments the second stage of the system may contain aplurality of air assisted atomisers, a source of water at low pressure,a modulating control valve that may substantially continuously providevariable water quantity, a source of air at low pressure, and amodulating control valve to substantially continuously provide variableair quantity. In some embodiments the source of the air at low pressuremay be a compressor. In other embodiments the second stage of the systemmay further contain a water holding tank with automatic level controlsand a fixed speed circulating water pump.

In other embodiments the second stage of the system may contain aplurality of high pressure nozzles and a fixed speed circulating waterpump.

In some embodiments the first stage control system of two-stage foggingsystem may utilize a set point of relative humidity that is calculatedaccording to filter differential pressure and relative humidity curves.The control system may utilize a set point of differential pressurewithin an expected operating range. The control system may utilize a setpoint of downstream temperature between ambient temperature and wet bulbtemperature. In all cases a closed loop control system is used toachieve the desired set point by adjusting the water flow rate to theatomisers.

In some embodiments the second control system of the two-stage foggingsystem may utilize an on/off switch operated by operator preference forsupplemental cooling to wet bulb temperature.

The present disclosure also includes a method of control for a two-stagefogging system that includes adding water droplets to the ambient airsupplied to a device via a filter house. The method of control for thefirst stage of the fogging system may include: controlling the waterflow rate to a plurality of first stage atomisers, measuring thedifferential pressure, and adjusting the rate of water to the firststage atomisers according to a set point of relative humidity. Themethod of control for the first stage of the fogging system may include:controlling the water flow rate to a plurality of first stage atomisers,and adjusting the rate of water to the first stage atomisers accordingto a pre-determined set point of relative humidity. The method ofcontrol for the first stage of the fogging system may include:controlling the water flow rate to a plurality of first stage atomisers,measuring the downstream temperature, and adjusting the rate of water tothe first stage atomisers according to a set point of downstreamtemperature. The method of control for the second stage of the foggingsystem may comprise turning a plurality of second stage nozzles on/offaccording to operator preference for supplemental cooling to wet bulbtemperature.

In some embodiments, the device to be combined with the two stage systemmay be selected from a group consisting of a gas turbine, diesel engine,process blower, other motive force, or general ventilation, clean room.

In some embodiments, the plurality of first stage atomisers may bepositioned about 1 meter upstream of the filter house. In otherembodiments, a plurality of first stage atomisers may be positionedupstream and adjacent the filter house. In other embodiments, aplurality of first stage atomisers may be positioned downstream of anumber of filter stages, and upstream of the final filter stage.

In some embodiments, the plurality of low capacity second stage foggers(e.g. atomiser or nozzles) may be positioned downstream of the filterhouse.

A two-stage system for reducing the inlet air temperature of a gasturbine is described, where a first stage comprises a high capacityfogging system positioned upstream of a filter that is capable ofachieving up to about 90% of the air cooling potential between ambienttemperature and wet bulb temperature, and a second stage comprises a lowcapacity fogging system positioned downstream of a filter that iscapable of achieving about 10% of cooling.

A two-stage fogging system for reducing the inlet air temperature of agas turbine that includes one or more filters. A first stage positionedupstream of the one or more filters and including one or more rotaryatomizers that is capable of achieving up to about 90% of the aircooling potential between ambient temperature and wet bulb temperature.A second stage positioned downstream of the one or more filters andincluding one or more nozzles that is capable of achieving about 10% ofthe supplemental air cooling towards wet bulb temperature.

A further embodiment is set forth including a method of control for afogging system for reducing the inlet air temperature of a gas turbine,wherein the method may comprise: introducing water droplets into the airupstream of the filter; measuring the ambient temperature, ambientrelative humidity, and ambient air pressure; measuring the temperature,relative humidity, and air pressure immediately following the filter;calculating the differential pressure value; maintaining a set relativehumidity after the filter, where the set relative humidity is determinedaccording to differential pressure/relative humidity curve; andcontrolling a water flow rate to achieve the set relative humidity,where increasing the water flow rate increases the relative humidity,and decreasing the water flow rate decreases the relative humidity.

A further embodiment is set forth including a method of control for afogging system for reducing the inlet air temperature of a gas turbine,wherein the method may comprise: introducing water droplets into the airupstream of the filter; measuring the ambient temperature, ambientrelative humidity, and ambient air pressure; measuring the temperature,relative humidity, and air pressure immediately following the filter;calculating the differential pressure value; maintaining a settemperature after the filter, where the set temperature is at a valuebetween ambient temperature and wet bulb temperature; and controlling awater flow rate to achieve the set temperature, where increasing thewater flow rate decreases the downstream temperature, and decreasing thewater flow rate increases the downstream temperature.

In some embodiments the set relative humidity may be about 80% to about95%. In other embodiments, the set relative humidity may be about 90%.

In some embodiments controlling the water flow rate may further compriseactuation of a modulating control valve.

In some embodiments controlling the water flow rate may further compriseactuation of a variable frequency drive pump.

In some embodiments, a system for reducing inlet air temperature of amotive force protected by air filtration may include a high capacityfirst stage fogging system and a low capacity second stage foggingsystem. The high capacity first stage fogging system upstream of one ormore inlet air filters provides a majority of total air cooling whereina first control system substantially continuously modulates water flowrate into the first stage fogging system to achieve a set relativehumidity to reduce inlet air temperature as compared to ambienttemperature. The low capacity second stage fogging system downstream ofthe one or more inlet air filters provides supplemental cooling to themajority of total air cooling of the first stage fogging system, whereina second control system controls supplemental cooling to wet bulbtemperature. The first stage fogging system achieves about 80% to about95% of the majority of total air cooling. A set relative humidity of thefirst control system may be calculated through selection of a point withhighest relative humidity on a differential pressure and relativehumidity curve prior to an exponential increase in differential pressureon the curve. A set point of minimum temperature after cooling of thefirst control system may be selected to avoid problems of capacityconstraint in downstream equipment due to high ambient temperature. Aset point of minimum temperature after cooling of the first controlsystem may be selected to avoid problems of icing at the compressor bellmouth. A set point of maximum filter differential pressure of the firstcontrol system may be selected as a fail-safe mechanism in the event ofa sudden increase of differential pressure due to environmentalconditions such as an ingress of hygroscopic material onto the filters.The second control system may utilize an on/off switch operated by anoperator preference for supplemental cooling to wet bulb temperature.The high capacity first stage fogging system may include a plurality ofrotary atomisers with variable frequency drive, a source of water at lowpressure, and a modulating control valve to substantially continuouslyprovide variable water flow rate. The high capacity first stage foggingsystem may include a water holding tank with automatic level controlsand a low pressure circulating water pump with variable frequency driveto provide substantially continuously variable water quantity. Thesource of air at low pressure may be a compressor. The high capacityfirst stage fogging system may include a plurality of medium pressurenozzles, a source of water at low pressure, a water holding tank withautomatic level controls, and a circulating water pump with variablefrequency drive to provide substantially continuously variable waterquantity. The low capacity second stage fogging system may include aplurality of air assisted atomisers, a source of water at low pressure,a modulating control valve to substantially continuously providevariable water quantity, a source of air at low pressure, and amodulating control valve to substantially continuously provide variableair quantity. The low capacity second stage fogging system may include aplurality of high pressure nozzles and a fixed speed circulating waterpump.

Another embodiment may include a two-stage fogging system for reducingthe inlet air temperature of a gas turbine. The two-stage fogging systemmay include one or more filters, a first stage, and a second stage. Thefirst stage may be positioned upstream of the one or more filters andinclude one or more rotary atomizers that is capable of achieving about90% of the air cooling towards wet bulb temperature. The second stagemay be positioned downstream of the one or more filters and include oneor more nozzles that is capable of achieving about 10% of thesupplemental air cooling towards wet bulb temperature.

Another embodiment may include a method of control for a fogging systemfor reducing the inlet air temperature of a device. The method mayinclude measuring the ambient temperature, ambient relative humidity,and ambient air pressure, introducing water droplets into the airupstream of the filter, measuring the temperature, relative humidity,and air pressure downstream from the filter, and calculating adifferential pressure value, maintaining a set relative humidity afterthe filter wherein the set relative humidity is determined according todifferential pressure relative humidity curves, and controlling a waterflow rate to achieve set relative humidity such that increasing thewater flow rate increases the relative humidity and decreasing the waterflow rate decreases the relative humidity. The set relative humidity maybe about 80% to about 95%. The set relative humidity may be about 90%.The step of controlling the water flow rate may include turning a valvea quarter-turn at a time. The device may be selected from a groupconsisting of a gas turbine, diesel engine, process blower, other motiveforce, general ventilation, clean room. Further, the set point ofrelative humidity may be calculated by selecting of a point with highestrelative humidity on a differential pressure and relative humidity curveprior to an exponential increase in differential pressure on the curve.

It should be appreciated that all combinations of the foregoing conceptsand additional concepts discussed in greater detail below provided suchconcepts are not mutually inconsistent are contemplated as being part ofthe subject matter disclosed herein. In particular, all combinations ofclaimed subject matter appearing at the end of this disclosure arecontemplated as being part of the subject matter disclosed herein.

According to that, in a preferred embodiment of the system according tothe invention the first stage fogging system achieves about 80% to about95% of the majority of total air cooling.

In another preferred embodiment, the set relative humidity of the firstcontrol system is calculated through selection of a point with highestrelative humidity on a differential pressure and relative humidity curveprior to a steep increase of the differential pressure or prior to anexponential increase in differential pressure on the curve.

In yet another embodiment a set point of minimum temperature aftercooling of the first or second? control system is selected to avoidproblems of capacity constraint in downstream equipment due to highambient temperature.

According to a further preferred embodiment, a set point of minimumtemperature after cooling of the first or second? control system isselected to avoid problems of icing at the compressor bell mouth.

In a further embodiment, a set point of maximum filter differentialpressure of the first control system is selected as a fail-safemechanism in the event of a sudden increase of differential pressure dueto environmental conditions such as an ingress of hygroscopic materialonto the filters.

Further preferred the second control system utilizes an on/off switchoperated by an operator preference for supplemental cooling to wet bulbtemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a gas turbine engine with a two-stagefogging system as may be described herein;

FIG. 2 is a graph showing measurements of downstream relative humidityas a function of modulating valve position, at ambient 70% relativehumidity before, during, and after first-stage fogging using the twostage fogging system described herein;

FIG. 3 is a graph showing the relationship between filter differentialpressure and relative humidity curve, for a typical in-service filterwhich would be downstream of the first stage fogging using the two stagefogging system described herein;

FIG. 4 is a graph showing filter differential pressure and relativehumidity curves using the two stage fogging system described herein;

FIG. 5 is a graph showing measurements of downstream temperature as afunction of modulating valve position, at ambient 14.3 degrees Celsiuswet bulb temperature before, during, and after first-stage fogging usingthe two stage fogging system described herein;

FIG. 6 is a graph showing measurements of the approach to wet bulbtemperature as a function of modulating valve position, at ambient 14.3degrees Celsius wet bulb temperature before, during, and afterfirst-stage fogging using the two stage fogging system described herein;

FIG. 7 is a perspective view of one embodiment of the two stage foggingsystem described herein for the rotary atomiser and control panelembodiment.

FIG. 8 is a graph showing measurements of inlet air conditions before,during, and after first-stage fogging using the two stage fogging systemdescribed herein;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter. Thisinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein; rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the invention to thoseskilled in the art.

As shown in FIG. 1, the inlet air cooling system 100 comprises twostages of fogging. The first stage of the two-stage fogging introduceswater, in the form of droplets, into the air stream before the one ormore air filters 120. This introduction of water droplets may occurthrough the use of one or more high capacity rotary atomisers 110. Thesehigh capacity rotary atomisers 110 may include an electric motor with awire cage around the exterior of the motor, such that when the waterpasses through the wire cage, the wire cage causes the water to breakinto small particles or droplets. Due to their high capacity nature, therotary atomisers are capable of providing a greater water flow rate, forexample as measured in litres of water per minute, to the air stream ascompared to traditional high pressure nozzles. For example, rotaryatomisers may provide about 0.5 to about 3.0 litres of water per minuteto the air stream at a droplet size of about 40 to about 70 microns,compared to traditional high pressure nozzles used for in-duct foggingwhere the average capacity is about 0.18 litres per minute. Further,rotary atomisers are capable of accepting a range of water qualitywithout detrimental effect. Therefore, the rotary atomizers do notrequire demineralized water and may use any available potable watersource. These rotary atomisers have variable frequency drives, and arecapable of running from 0% to 100% capacity without affecting the sizeof the droplets.

Alternatively, other fog generating devices may be used for theintroduction of water droplets during the first stage of fogging. Forexample, medium pressure nozzles or air assisted atomisers that operatebetween about 5 and about 20 bar can be controlled within acceptableconstraints of the droplet size, for example 40 to 70 microns. Thecurrent state of the art rotary atomisers may not be suitable for use insome environments, such as for example, but is not limited to, explosionproof environments (e.g. refineries). In these types of environments ahigh capacity nozzle with an explosion-proof pump may be alternativelyused to achieve the first-stage cooling.

Rotary atomisers 110, or alternate first stage fog generation devices,are placed upstream of the one or more filters 120. Generally, therotary atomisers 110 are placed about 1 meter upstream of the filters,which may place them inside of a weather hood or even in the filterhouse, depending on the dimensions of the particular set-up. Thepositioning of the atomisers before the filtering media of about 1 meterallows for the water to evaporate before hitting the filter, preventingthe filter from becoming saturated with water. However, if the filterutilizes a droplet catcher (such as for example AAF International'sAmerDrop system) or a weather louver (such as for example AAFInternational's AmerVane product) then the placement of the atomiser maybe immediately upstream of the filter within the filter house.Additionally, where a filter has a hydrophobic coalescing media (such asfor example AAF International's AMERSHIELD and AMERKOOL products),containing glass fibres and oils, the moisture will coalesce to formlarger droplets which drain out of the airstream, which may also allowthe placement of the atomiser to be immediately upstream of the filterwithin the filter house. Preferably, the filter contains some device orcoating that protects the filter from condensation, droplets, or waterhitting the filter, which may cause an increase in differentialpressure. More preferably, the filter contains a coalescing part or aweather louver, such that water is prevented from passing through thefilter without a decrease in differential pressure. The use of thesehydrophobic filters allows for the first-stage fogging system to enactevaporative cooling with negligible risk of water downstream of the oneor more filters 120, protecting the compressor's 10 intake.

Unlike conventional high pressure nozzles used downstream of the filterhouse, the volume and flow rate of water supplied to the first-stagefogger (such as for example a rotary atomizer) may be controlled througha modulating control valve 140, for example a globe valve or a smalltank with a variable frequency drive pump attached, without affectingdroplet particle size. The first controller or control system 150receives signals, in the form of, for example, measurements oftemperature, relative humidity, and pressure from both one or moresensors 152, 154 located before the filter 120 and one or more sensors156 after the filter 120. Measurement of the pressure before and afterthe filter allows for the controller to calculate the differentialpressure. Differential pressure is a calculation of the differencebetween the pressures measured at two points, here, the points arebefore the filter and after the filter. The first controller 150utilizes these measurements in order to control the flow rate of watersupplied in order to reach a desired relative humidity, with reducedaffect to differential pressure. Differential pressure is a calculationof the difference between the pressures measured at two points; here,the two points are before the filter and after the filter. For examplein a system where pressure is measure before and after the filter stagewater hitting the filter may cause an increase in differential pressure.A closed loop substantially continuously controls or modulates the waterflow rate from the relative humidity measurements. Additionally, it isalso possible to control the system to regulate downstream temperatureand differential pressure. Control of downstream temperature may bedesired due to capacity constraints of downstream equipment (for examplean alternator) at high ambient temperature. For example, selecting a setpoint of minimum temperature after cooling of the first control systemmay avoid problems of capacity constraint in downstream equipment due tohigh ambient temperature. Further by example, selecting a set point ofminimum temperature after cooling of the first control system may avoidproblems of icing at the compressor bell mouth. Also, a set point ofmaximum filter differential pressure of the first control system isselected as a fail-safe mechanism in the event of a sudden increase ofdifferential pressure due to environmental conditions such as an ingressof hygroscopic material onto the filters.

Generally, the first-stage fogging system is controlled throughmaintaining a set point of relative humidity, determined according tofilter differential pressure and relative humidity curves. It has beenobserved that downstream relative humidity can be controlled preciselyby manually or automatically controlling water flow rate. FIG. 2 shows astraight line relationship between relative humidity and valve position.FIG. 2 is an example observation where the ambient relative humidity was70%, and the downstream relative humidity was adjusted up to 90%. Thisset relative humidity is calculated through selection of a point fromfilter differential pressure and relative humidity curves, as shown inFIG. 3 and FIG. 4. The differential pressure and relative humidity curveof FIG. 3 is generated by plotting the relative humidity (x-axis) by thedifferential pressure (y-axis). The curve shows the relationship ofbetween these two variables, for example the differential pressure mayremain constant while relative humidity increases. These curves indicateat what relative humidity measurement, or range of measurements, thedifferential pressure may increase. This allows for the controller toset the point with a maximum relative humidity as high as possiblewithout affecting differential pressure. FIG. 3 shows the relationshipbetween differential pressure and relative humidity for a mini-pleatfilter with hydrophobic media, with data gathered between 4000 and 5000running hours.

As shown in FIG. 4, the filter differential pressure and relativehumidity curves may be different for various types of filters, such asAAF's HydroVee filter 410 or AAF's AstroCel filter 420 or AAF's DuraCelfilter 430. However, as generalized in FIGS. 3 and 4 there is anincrease in the filter differential pressure as relative humidityreaches about 90%. Therefore, the target relative humidity should bepreferably set at about 80% to about 95%. Even more preferably thetarget relative humidity should be set at about 90%. The first-stagefogging system, which can finely control relative humidity, can be usedto control the temperature and relative humidity without causing spikesof differential pressure. To achieve this temperature control, the waterflow rate may be finely controlled through small incremental turns ofthe modulating control valve 140. This fine control of the water flowrate, combined with set maximum relative humidity (as determined bydifferential pressure relative humidity curves) allows the firstcontroller 150 to finely control the temperature, such that when thewater flow rate is increased slightly, the relative humidity increasesslightly and thus the temperature also decreases slightly.

FIG. 5 shows a straight line relationship between downstream temperatureand valve position for a given set of ambient conditions. This indicatesthat a set point temperature between ambient temperature and wet bulbtemperature can be controlled by adjusting the water flow rate throughcontroller 150. The control system can therefore be set to provide adepressed temperature after cooling, with an automatic maximum relativehumidity which avoids deleterious effects on filter differentialpressure.

A thermal efficiency measurement indicates the efficiency of evaporativecooling of the first-stage fogging (e.g. rotary atomisers). Thermalefficiency is calculated as follows:

${{Thermal}\mspace{14mu} {Efficiency}} = \frac{{{ambient}\mspace{14mu} {temperature}} - {{measured}\mspace{14mu} {temperature}}}{{{ambient}\mspace{14mu} {temperature}} - {{wet}\mspace{14mu} {bulb}\mspace{14mu} {temperature}}}$

As the water flow rate increases, the relative humidity increases inproportion, as the thermal efficiency trends with relative humidity.Further, the relationship between thermal efficiency and water flow rateis mostly linear, such that when the water flow rate increases, so doesthe thermal efficiency. Therefore, in this two-stage cooling system,about 90% of the total cooling achieved by the system may be achievedthrough the first-stage fogging system (for example through the use ofrotary atomisers). The first stage fogging system has been demonstratedto achieve 100% thermal efficiency at high relative humidity. Bycontrolling set point relative humidity to approximately 90%, the firststage fogging is deliberately constrained to approximately 90%efficiency.

An alternate measure of evaporative cooling efficiency, particularlyuseful in moderate climates, is the approach to wet bulb temperature.FIG. 6 shows first stage fogging system achieving an approach of lessthan 0.5 degrees Celsius, with a linear relationship between valveposition (water flow rate) and approach to wet bulb temperature.

In particular instances it may be preferable to maintain a certaintemperature downstream of the filter, in these instances the firstcontrol system may limit the flow rate of water in order to achieve aparticular downstream temperature based on site requirements at eachstage. This allows for fine control in situations where the ambienttemperature is high and extra power is desired, but generator output isthe constraining variable in a gas turbine power generation set.Additionally, where there is a marked change in the differentialpressure, or when differential pressure falls outside of a specifiedrange, the control system 150 may be programmed to set an alarm oralternatively make proactive in-line modifications such as to trim thewater flow rate. This alarm or indicator may be any kind of alarm ornotification, including visual, audible, or any combination of the two.However, due to dust and particle build up from incoming air in thefilter, the differential pressure increases with the age. For example,the differential pressure may increase a few Pascals from when thefilter was new as compared to a filter aged to about 12 to about 24months old. Therefore, a static control utilizing a set differentialpressure is not preferable.

In some embodiments the first-stage fogging system may have a source oflow pressure water and a modulating control valve 140 to substantiallycontinuously provide variable water quantities. In other embodiments thesystem may further comprise a water holding tank with automatic levelcontrols and a fixed speed circulating pump.

In some embodiments the first stage fogging system may have a source oflow pressure water, a water holding tank with automatic level control,and a low pressure circulating water pump with variable frequency drivein order to substantially continuously provide variable water quantity.

Front-facing or first stage fogging systems may be installed orretrofitted onto existing filter housings. For retrofitting, a frame maybe placed inside of the weather hood or inside the filter house to whichthe first-stage foggers are attached. Alternatively first stage foggersmay be supported directly on the same pipe which supplies water to eachfogging unit. Sensors that measure the relative humidity, temperature,and pressure may be placed before the one or more filters 703 such aswith sensors 152, 154 and after the one or more filters with sensor 156.Sensors may be connected to the control system 150 or in communicationtherewith. As shown in FIG. 7, where retrofitted, the first stagefogging devices 702 may be supported on the supply pipe 50 insideweather hoods 701 or a filter house 704. One embodiment uses amodulating control valve 707, actuated via the control system 150.Retrofitting allows for the use of existing systems, reducesinstallation time, and eliminates the need to shut down the gas turbinefor installation or for inspection of the front facing foggers. Thefirst-stage fogging system achieves fine control of inlet air relativehumidity and temperature, while maintaining downstream filterdifferential pressure in an acceptable range. Additionally, the finecontrol of the first-stage fogging system may prevent problems withover-supply of water often seen in state of the art systems.

The second stage of the two-stage fogging introduces water, in the formof droplets, into the air stream after the air filters 120 from one ormore plurality of low capacity nozzles 160 to provide supplementalcooling towards the wet bulb temperature. These low capacity nozzles maybe high pressure nozzles, or alternatively may be air assisted nozzles.In embodiments utilizing high pressure nozzles, a water tank withautomatic level control and a fixed speed circulating pump may be used.In embodiments utilizing air assisted nozzles, a source of air at lowpressure, such as an air compressor, and a modulating control valve 140to substantially continuously provide variable air quantity may be used.Generally, however, these second stage delivery systems provide water ata significantly reduced flow rate as compared to the first stage.

Due to the efficiency of the first-stage fogging, using for example oneor more rotary atomisers 110 which achieve about 90% of the totaltwo-stage system cooling, only a small plurality of low capacity nozzles160 may be used in the second fogging stage to supplement cooling to thewet bulb temperature. The second stage of the cooling may be desired toachieve only about 10% of the total cooling, this reduced cooling loaduses a small plurality of nozzles to achieve.

These low capacity nozzles 160 may be controlled through a secondcontroller or control system 170 reduced to a binary (on/off) function.The decision to turn the second stage fogging on or off may be dependenton ambient relative humidity or a plant operator decision regardingwhether the air inlet to the drive requires supplemental cooling to thewet bulb temperature from the second-stage system. For example, thisbinary control system may switch on or off when the temperature, asmeasured by the sensor 156 after the filter 120, is above a set value.The low capacity nozzles 160, because of their small plurality, may bepositioned around the periphery of the duct at the location downstreamof one or more filters 120. Positioning the nozzles 160 around theperiphery of the duct decreases complexity of the system, which reducesthe cost and downtime required for the installation and maintenance ofthe nozzles. Additionally, the minimization of hardware in the clean airstream decreases the risk of a foreign object (for example metal from anozzle) falling into the gas turbine engine or system 20.

While several inventive embodiments have been described and illustratedherein, those of ordinary skill in the art will readily envision avariety of other means and/or structures for performing the functionand/or obtaining the results and/or one or more of the advantagesdescribed herein, and each of such variations and/or modifications isdeemed to be within the scope of the invent of embodiments describedherein. More generally, those skilled in the art will readily appreciatethat all parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the inventive teachingsis/are used. Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, many equivalentsto the specific inventive embodiments described herein. It is,therefore, to be understood that the foregoing embodiments are presentedby way of example only and that, within the scope of the appended claimsand equivalents thereto, inventive embodiments may be practicedotherwise than as specifically described and claimed. Inventiveembodiments of the present disclosure are directed to each individualfeature, system, article, material, kit, and/or method described herein.In addition, any combination of two or more such features, systems,articles, materials, kits, and/or methods, if such features, systems,articles, materials, kits, and/or methods are not mutually inconsistent,is included within the inventive scope of the present disclosure.Further, it is to be understood that continuously or substantiallycontinuously may include one or more interruptions, delays, etc. incontrolling characteristics such as but not limited to the quantities,rates, measurements disclosed herein and still be within the scope ofthe embodiments. Alternatively, control or adjustments may be consideredor provided intermittently.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms. The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.” When used in thisdescription and the claims as an adjective rather than a preposition,“about” means “approximately” and comprises the stated value and everyvalue within 10% of that value. For example, “about 100%” would includemeasurements of 90% and 110%, as well as every value in between. Thephrase “and/or,” as used herein in the specification and in the claims,should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases.

Multiple elements listed with “and/or” should be construed in the samefashion, i.e., “one or more” of the elements so conjoined. Otherelements may optionally be present other than the elements specificallyidentified by the “and/or” clause, whether related or unrelated to thoseelements specifically identified. Thus, as a non-limiting example, areference to “A and/or B”, when used in conjunction with open-endedlanguage such as “comprising” can refer, in one embodiment, to A only(optionally including elements other than B); in another embodiment, toB only (optionally including elements other than A); in yet anotherembodiment, to both A and B (optionally including other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

The foregoing description of several methods and embodiments have beenpresented for purposes of illustration. It is not intended to beexhaustive or to limit the precise steps and/or forms disclosed, andobviously many modifications and variations are possible in light of theabove teaching. It is intended that the scope and all equivalents bedefined by the claims appended hereto.

EXAMPLES Example 1

An on-plant inlet cooling trial was conducted demonstrating that thefirst stage fogging, and associated control system, may controltemperature and relative humidity by simply adjusting the water flowrate to the first-fogging system (e.g. rotary atomiser). The trial beganby first allowing the inlet conditions to stabilize before the rotaryatomiser was turned on. After the inlet conditions stabilized the rotaryatomiser was started with a water flow rate of 0.5 litres per minute (Aof FIG. 8), at this point the temperature immediately begins to dropfrom about 19.5° C. to about 18.2° C. and the inlet air relativehumidity increases from about 76% to about 84%. An additional increasein water flow rate to 0.7 litres per minute (B of FIG. 8) is tested, andfollowing this increase in the water flow rate the temperature continuesto decrease to about 17.5° C. and the inlet air relative humidityincreases to about 92%. Incremental decreases in the water flow rate to0.5 litres per minute (C of FIG. 8) then 0.3 litres per minute (D ofFIG. 8), and each cause a slight decrease in the temperature, whilerelative humidity remained constant. These incremental changes in thewater flow rate allows for finer control of the temperature and relativehumidity. Once the water flow is turned off (E of FIG. 8) the relativehumidity and temperature slowly return to ambient inlet airmeasurements. This data indicates that the first-stage fogging system(e.g. rotary atomisers) produce a nearly immediate reduction intemperature and relative humidity. This on-plant test indicates that arelative humidity of about 97% may be achieved within 10 minutes of thesystem being started.

Example 2

Pressure measurements were taken both before and after the filter houseduring the on-plant inlet cooling trial as conducted in example 1allowing the differential pressure to be calculated. When the water ratewas increased from 0.5 litres per minute to 0.7 litres per minute (B ofFIG. 8) the differential pressure begins to increase to its peak of 460Pascals. This maximum is reached and began declining prior to theincremental decrease of the water flow rate to 0.5 litres per minute (Cof FIG. 8). The differential pressure continued to decrease until theafter the water flow is turned off (E of FIG. 8), where it stabilizes atabout 434 Pascals. The differential pressure measurements can be plottedagainst the relative humidity to generate a curve showing at whatrelative humidity measurement the differential pressure increases. Thedifferential pressure relative humidity curve for EXAMPLES 1 and 2 isdepicted in FIG. 4. The differential pressure remained constant atapproximately 430 Pascals while the relative humidity increased, untilthe relative humidity measured approximately 87%, at which point thedifferential pressure begins to increase at an exponential rate.

Example 3

In an embodiment of the two-stage cooling system herein, the ambienttemperature at the inlet of the air cooling system was measured at about50° C. Rotary atomisers were used to generate fog in the first stage offogging. A maximum relative humidity of 90% (as determined by thedifferential pressure relative humidity curve) cooled the air to about26° C. (a 24° C. temperature drop from the ambient air temperature). Thesecond-stage fogging utilized a small plurality of low capacity highpressure nozzles, which provided further cooling of the air to about 24°C. (an additional 2° C. decrease in temperature). The air temperaturedropped by a total 26° C. through use of the two-stage system, themajority (about 92%), of which occurred in the first fogging stage.Further, due to the cooling capacity of the first-stage fogging, therewas no need to provide overspray cooling in the axial compressor at thecompressor inlet.

Finally summarizing, the inventions also refers to a system for reducinginlet air temperature of a motive force protected by air filtration,comprising: a high capacity first stage fogging system upstream of oneor more inlet air filters that provides a majority of total air cooling,wherein a first control system substantially continuously modulateswater flow rate into the first stage fogging system to achieve a setrelative humidity to reduce inlet air temperature as compared to ambienttemperature; and a low capacity second stage fogging system downstreamof the one or more inlet air filters that provides supplemental coolingto the majority of total air cooling of the first stage fogging system,wherein a second control system controls supplemental cooling to wetbulb temperature.

The first stage fogging system preferably achieves about 80% to about95% of the majority of total air cooling.

The set relative humidity of the first control system is preferablycalculated through selection of a point with highest relative humidityon a differential pressure and relative humidity curve prior to anexponential increase in differential pressure on the curve.

A set point of minimum temperature after cooling of the first controlsystem is preferably selected to avoid problems of capacity constraintin downstream equipment due to high ambient temperature.

A set point of minimum temperature after cooling of the first controlsystem is preferably selected to avoid problems of icing at thecompressor bell mouth.

A set point of maximum filter differential pressure of the first controlsystem is preferably selected as a fail-safe mechanism in the event of asudden increase of differential pressure due to environmental conditionssuch as an ingress of hygroscopic material onto the filters.

The second control system preferably utilizes an on/off switch operatedby an operator preference for supplemental cooling to wet bulbtemperature.

The high capacity first stage fogging system preferably comprises: aplurality of rotary atomisers with variable frequency drive;

a source of water at low pressure; and a modulating control valve tosubstantially continuously provide variable water flow rate.

The high capacity first stage fogging system preferably furthercomprises: a water holding tank with automatic level controls; and a lowpressure circulating water pump with variable frequency drive to providesubstantially continuously variable water quantity.

The source of air at low pressure preferably is a compressor.

The high capacity first stage fogging system preferably comprises: aplurality of medium pressure nozzles; a source of water at low pressure;a water holding tank with automatic level controls; and a circulatingwater pump with variable frequency drive to provide substantiallycontinuously variable water quantity.

The low capacity second stage fogging system preferably comprises: aplurality of air assisted atomisers; a source of water at low pressure;a modulating control valve to substantially continuously providevariable water quantity; a source of air at low pressure; and, amodulating control valve to substantially continuously provide variableair quantity.

The low capacity second stage fogging system preferably comprises: aplurality of high pressure nozzles; and a fixed speed circulating waterpump.

A two-stage fogging system for reducing the inlet air temperature of agas turbine comprising: one or more filters; a first stage positionedupstream of the one or more filters and including one or more rotaryatomizers that is capable of achieving about 90% of the air coolingtowards wet bulb temperature; and a second stage positioned downstreamof the one or more filters and including one or more nozzles that iscapable of achieving about 10% of the supplemental air cooling towardswet bulb temperature.

Additionally, the inventions also refers to a method of control for afogging system for reducing the inlet air temperature of a driver,wherein the method comprises: measuring the ambient temperature, ambientrelative humidity, and ambient air pressure; introducing water dropletsinto the air upstream of the filter; measuring the temperature, relativehumidity, and air pressure downstream from the filter; calculating adifferential pressure value; maintaining a set relative humidity afterthe filter, wherein the set relative humidity is determined according todifferential pressure relative humidity curves; and controlling a waterflow rate to achieve set relative humidity, such that increasing thewater flow rate increases the relative humidity and decreasing the waterflow rate decreases the relative humidity.

The set relative humidity preferably is about 80% to about 95%.

The set relative humidity preferably is about 90%.

Controlling the water flow rate further preferably comprising turning avalve a quarter-turn at a time.

The driver is preferably selected from a group consisting of a gasturbine, diesel engine, process blower, or other motive force.

The set point of relative humidity preferably is calculated by selectingof a point with highest relative humidity on a differential pressure andrelative humidity curve prior to an exponential increase in differentialpressure on the curve.

1. A method of running an air inlet system upstream of one or more inletair filters of a device protected by air filtration, wherein the methodcomprises: regulating the relative air humidity of the inlet air at theone or more inlet air filters in dependence of the inlet air filtersdifferential pressure.
 2. The method of claim 1, wherein the relativeair humidity is set to amount between 70% and 90%, in particular between75% and 85%.
 3. The method of claim 2, wherein the relative air humidityis set to amount about 80%.
 4. The method of claim 1, wherein therelative air humidity is to be set by means of a cooling system.
 5. Themethod of claim 4, wherein the cooling system includes an evaporativecooling system.
 6. The method of claim 5, wherein the evaporativecooling system includes a fogging system.
 7. The method of claim 6,wherein the fogging system includes at least one rotary atomiser.
 8. Themethod of claim 4, wherein the cooling system includes two coolingstages, in particular a first stage fogging system upstream of one ormore inlet air filters and a second stage fogging system downstream ofthe one or more inlet air filters.
 9. The method of claim 8, wherein thesecond cooling stage regulates the relative air humidity to be about100%.
 10. The method of claim 1, wherein the relative air humidity is tobe set by means of a heating system.
 11. The method of claim 10, whereinthe heating system provides heat by means of warm air to be deliveredinto the inlet air.
 12. The method of claim 11, wherein the warm airincludes compressor bleed air.
 13. The method of claim 11 or 12, whereinthe warm air includes exhaust air of a motive device enclosure, inparticular a turbine enclosure.
 14. The method of claim 11, wherein thewarm air includes turbine exhaust air.
 15. The method of claim 10,wherein the heating system provides heat by means of a heat exchanger.16. The method of claim 10, wherein the heating system provides heat bymeans of a heater, in particular an electrical heater or a burner. 17.The method of claim 1, wherein the device is selected from a groupconsisting of a gas turbine, diesel engine, process blower, other motiveforce, or general ventilation, clean room.
 18. A system for reducinginlet air temperature of a device protected by air filtration,comprising: a first stage fogging system upstream of one or more inletair filters that provides inlet air cooling, wherein a first controlsystem controls cooling to achieve a set relative humidity of the inletair; and a second stage fogging system downstream of the one or moreinlet air filters that provides supplemental cooling to the first stagefogging system, wherein a second control system controls supplementalcooling to wet bulb temperature of the inlet air.